In tube mills, intermediate walls serve the purpose of separating the grinding media charge of adjacent grinding chambers from one another and of transporting the material being ground from one chamber to the other. For this purpose, a discharge means is usually disposed in the intermediate wall, and through this discharge means, the material being ground which passes via inlet openings into the intermediate chamber is transported via discharge openings into the second grinding chamber.
Discharge chambers are disposed at the end of the tube mill and are also equipped with a discharge means in order to discharge the finished ground material.
From DE-C-26 13 062, a lifting wall for a tube mill is known which comprises:                a front face which is provided in inlet openings through which material being ground passes into the wall,        a rear face with discharge openings through which the material being ground which is located in the lifting wall is discharged,        a central air duct for an air stream which is led through the tube mill, wherein the air duct has an air intake opening in the front face and an air outlet opening in the rear face of the lifting wall and the discharge openings are disposed in an annular region around the air outlet opening,        and a discharge means.        
The discharge means has lifting vanes which are adjustable in the radial direction. Due to the rotary movement of the tube mill, the material being ground is lifted upwards over the lifting vanes and then slides thereon to the enter where it is discharged through the discharge openings.
In DE-B-22 07 484, a lifting wall is proposed in which the volume of the lifting vanes can be altered by rotation of the vanes. In another embodiment from this publication, in the region of the discharge opening of the intermediate wall, there is disposed a truncated cone with a movable closure ring which, depending upon its position, allows a greater or a lesser discharge of material being ground.
However, the known discharge means have the disadvantage that the material being ground which is transported via the lifting vanes to the center is discharged in such a way that it is fed into the air stream which is led through the tube mill. This in turn leads to a situation where the discharged material being ground does not pass immediately after the intermediate wall into the ball charge of the second grinding chamber but rather is pneumatically introduced more or less far into the second grinding chamber. However, as a result, the ball charge is not fully utilised, which results in reduced efficiency.